Method for operating a packet based data network

ABSTRACT

A method for operating a packet based data network ( 21; 31 ), the data network ( 21; 31 ) comprising a multitude of nodes (A, B, C, D) and a shared data bus ( 22; 32 ), wherein at least some of the nodes (A, B, C, D) add traffic to the data bus ( 22; 32 ), and wherein the upstream nodes (A, B, C, D) reserve data transfer capacity of the data bus ( 22; 32 ) for downstream nodes (A, B, C, D) by means of a fairness mechanism, is characterized in that at least some of the nodes (A, B, C, D) drop traffic from the data bus ( 22; 32 ), and that said fairness mechanism takes into account the drop traffic at downstream nodes (A, B, C, D). The inventive method allows a better bandwidth utilization and uses available resources more efficiently.

The invention is based on a priority application EP 605290863.9 which ishereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a method for operating a packet based datanetwork, the data network comprising a multitude of nodes and a shareddata bus, wherein at least some of the nodes add traffic to the databus, and wherein with respect to a data flow in one direction of thedata bus, the upstream nodes reserve data transfer capacity of the databus for downstream nodes by means of a fairness mechanism.

BACKGROUND OF THE INVENTION

Such a method is described in L. Ciavaglia, N. Bouadallah, E. Dotaro andN. Le Sauze, “Matching Fairness and Performance by Preventive TrafficControl in Multiple Access Networks”, Opticom, Dallas, Tex., USA,October 2003.

A data network is used for transferring data from one place to another.For this purpose, the network comprises nodes, i.e. devices forreceiving data from and/or for feeding data into the network, and datatransfer lines connecting the nodes. The data transfer lines are calledbuses.

A data bus has a direction towards which the signals carrying the datamove on the bus. The nodes are situated along the bus. A node mayreceive data originating from nodes located upstream, i.e. located inthe direction where signals come from, and a node may send data to nodeslocated downstream, i.e. located in the direction towards which signalsmove on the bus.

A bus has a limited data transfer capacity, caused e.g. by the limitedbandwidth of a channel. Therefore, when data is to be added to the busat a node, the node needs free data transfer capacity on the bus to doso. Without any measures, nodes located at or near the upstream end ofthe bus have a relatively easy access to the bus, whereas nodes locatedat or near the downstream end of the bus may have difficulties to finddata transfer capacity not already used by upstream nodes.

For this reason, a fairness mechanism may be applied. The fairnessmechanism makes upstream nodes (i.e. nodes with respect to which furthernodes located downstream exist) reserve data capacity for downstreamnodes (i.e. nodes with respect to which further nodes located upstreamexist). Then downstream nodes will find free data transfer capacity onthe bus.

L. Ciavaglia et al. describe an access control mechanism for amultipoint-to point network, comprising a plurality of nodes only addingdata to a bus, and a single node only dropping data from the bus. Ituses a preventive anti-token mechanism to grant access to the bus. Ananti-token forbids a node to emit data traffic for a given amount oftime, thus preserving voids for downstream nodes. For every node, afixed amount of data transfer capacity is reserved, according to aService Level Agreement (SLA). So every node will find some free datatransfer capacity of the bus. A node may also benefit from unusedreserved data transfer capacity of upstream nodes.

The disadvantage of this known method is a large amount of unused datatransfer capacity (i.e. bandwidth) on the bus, in particular near theupstream end of the bus. Only at the downstream end of the bus, its fulldata transfer capacity may be used.

It is therefore the object of the invention to improve said method toallow a better bandwidth utilization, and to use available resourcesmore efficiently.

SUMMARY OF THE INVENTION

This object is achieved, according to the invention, by a method asmentioned in the beginning, characterized in that at least some of thenodes drop traffic from the data bus, that said fairness mechanism takesinto account the drop traffic at downstream nodes, and that the fairnessmechanism applies anti-tokens at the nodes which add traffic to the bus,wherein the anti-tokens forbid a node to emit data traffic for a givenamount of time, thus preserving voids for nodes located downstream.

In a multipoint-to-multipoint network, at least some of the intermediatenodes have a drop function, too. Data traffic dropped at an intermediatenode principally causes a regain of available data transfer capacitydownstream of said intermediate node. Therefore, the regained datatransfer capacity can be used, in particular for adding data to the busat the intermediate node or downstream nodes and/or for reserving datatransfer capacity for downstream nodes that does not need to be reservedbefore the intermediate node. Since the fairness mechanism distributesthe data transfer capacity to the nodes, an increase of the utilizationof the data transfer capacity of the bus can be achieved by taking intoaccount the drop traffic when allocating data transfer capacity to thenodes.

According to the invention, the fairness mechanism (or fairnessalgorithm, or traffic control mechanism, or bandwidth allocationmechanism) is realized with anti-tokens. The function of anti-tokens, asthey are used with this invention, is described in EP 1 401 156 A2, thecontent of which is herewith incorporated by reference. The anti-tokenmechanism implies duties to nodes not to emit traffic (in contrast to arate limiter mechanism which grants rights to emit traffic).

In more detail, the upstream nodes regulate their traffic emission basedon the evaluation of the bandwidth demands of downstream nodes. Theregulation of the traffic emission of upstream nodes consists inpreserving free bandwidth for downstream nodes, in the proportion oftheir traffic demands, by forbidding the emission in upstream nodes. Theregulation of the traffic emission in upstream nodes is based on apreventive traffic control process which uses “anti-tokens” to allocatefree bandwidth for downstream nodes in priority to the traffic emissionof upstream nodes. The anti-token generation is calculated in eachupstream node by the bandwidth allocation controller of the node foreach segment of the shared data bus, taking into account the trafficadded to, and the traffic dropped from the shared data bus by thedownstream nodes. In particular, token buckets can be used to achievefair transmission rates for the nodes.

In a preferred variant of the inventive method,R_(i)=A_(i+1)−D_(i+1)+R_(i+1) for at least some of the nodes, with i:node index number, wherein the index numbers increase in downstreamdirection of the data traffic; R_(i): reserved data capacity at node ifor downstream nodes; A_(i+1): added traffic at node i+1, wherein nodei+1 is the neighbouring node of node i on the data bus in downstreamdirection; D_(i+1): dropped traffic at node i+1; R₁₊₁: reserved datacapacity at node i+1. Preferably, the above formula applies to all nodesi=[1, . . . , N], with N: number of nodes on the bus; if applicableprovided that for the node N at the downstream end of the bus A_(N)=0and R_(N)=O, and for the second to last node N−1 at the downstream endof the bus R_(N−1)=0. With this variant, the bandwidth reserved fordownstream nodes is minimized in upstream areas of the bus. The amountof reserved data transfer capacity is adapted flexibly to the actualdata traffic.

Another variant of the inventive method is characterized by a terminalnode at the downstream end of the data bus, wherein data traffic is onlydropped at the terminal node, and no data traffic is added at theterminal node. All traffic not dropped at intermediate notes is droppedat the terminal node. This variant keeps the network design simple. Inan inventive alternative to this variant, the data bus is a ring buswith no defined end or beginning.

In an advantageous variant of the inventive method, in each node on thedata bus, an opto-electronic conversion of all data traffic is done. Bythis means it is particularly simple to drop data out of the data buselectronically, but transfer data via the bus optically.

A highly preferred variant of the inventive method is characterized inthat in at least some of the nodes, traffic from the data bus, i.e.transit traffic, and add traffic of the node can be processed, whereinthe transit traffic and/or the add traffic comprise at least twopriority levels, in particular priority and best effort, and that thefairness mechanism takes into account the origin of the traffic, i.e.transit or add traffic, as well as the priority level of the traffic.This allows a more purposeful use of the data bus. In particular, it ispossible to reserve data transfer capacity only for add premium trafficof downstream nodes, what keeps a larger amount of data transfercapacity commonly available.

In a further development of the above variant, the node has a priorityorder of

I) transit premium traffic

II) reserved data capacity for downstream nodes

III) add premium traffic

IV) transit best effort traffic

V) add best effort traffic,

or a priority order of

I) transit traffic

II) reserved data capacity for downstream nodes

III) add premium traffic

IV) add best effort traffic,

wherein I) indicates highest priority. With these priority orders, goodflow of data has been found in simulation experiments.

A particularly advantageous variant of the inventive method ischaracterized in that the add traffic at a node is split into logicalpaths according to the destination of the add traffic, and that afairness mechanism is applied to each logical path to determine the datatransfer capacity available for the respective logical path. Thisvariant allows the direct control of data transfer between every pair oftwo nodes. This allows an even more efficient use of the data transfercapacity of the bus.

In a preferred further development of said variant, add traffic of alogical path of a first node with a destination not farther than asecond node located anywhere downstream of the first node is added tothe data bus independently from both the add traffic at the second nodeand the data capacity to be reserved downstream of the second node. Notethat said first and second node may, but do not need to be neighbouringnodes on the bus. With this further development, a free data transfercapacity on the bus only available between the first and second node canbe used for traffic added at the first node with a destination notfarther than the second node. This allows the use of reserved bandwidthat upstream nodes as long as the reserved bandwidth is not yet needed.This makes the use of the data transfer capacity more efficiently.

Within the scope of the invention is also a node for adding traffic to ashared data bus of a packet based data network, characterized by meansfor splitting add traffic into logical paths according to thedestination of the add traffic, and means for applying a fairnessmechanism to each logical path to determine a data transfer capacityavailable for the respective path, wherein the fairness mechanismapplies anti-tokens at the node, and wherein the anti-tokens forbid thenode to emit data traffic for a given amount of time. Such a node can beused in carrying out the above mentioned variant of the inventivemethod. The node provides means for controlling access to the datatransfer capacity, i.e. the resources, on a shared bus.

Further in the scope of the invention is a data network managementsystem for performing all the steps of the inventive method as describedabove. The network management system determines anti-tokens at the nodeswhich add traffic to the bus.

Further advantages can be extracted from the description and theenclosed drawing. The features mentioned above and below can be used inaccordance with the invention either individually or collectively in anycombination. The embodiments mentioned are not to be understood asexhaustive enumeration but rather have exemplary character for thedescription of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is shown in the drawing.

FIG. 1 shows a multipoint-to-point network architecture of the state ofthe art;

FIG. 2 shows a multipoint-to-multipoint network architecture for usewith the inventive method;

FIG. 3 shows a multipoint-to-multipoint network with a TCARDdistribution in accordance with the invention.

FIG. 4 shows a quality of service (QoS) model for use with theinvention, taking into account the origin of data only;

FIG. 5 shows another QoS model for use with the invention, taking intoaccount the origin of data and priority levels of data of all origins ofdata;

FIG. 6 shows another QoS model for use with the invention, taking intoaccount the origin of data and priority levels of data originating fromthe local node (=add traffic).

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to an improved fairness mechanism for accesscontrol to multipoint-to-multipoint networks.

Fairness mechanisms are known from the state of the art for amultipoint-to-point network. Such a network is shown in FIG. 1. Themultipoint-to-point network 11 comprises four nodes A, B, C, D, and ashared data bus 12. The overall data flow is directed towards note D atthe end of the data bus 12. At nodes A, B, C, data is fed into the bus12, as marked with add A, add B, add C. At the end node D, all data isdropped out of the network 11.

The data bus 12 has only a limited data transfer capacity. In order toguarantee that the intermediate notes B, C have the possibility to add aminimum amount of data to the bus 12, part of the data transfer capacityof the data bus 12 is reserved for the nodes B, C. This is done by meansof a so called traffic control architecture using remote descriptors(TCARD) which uses a preventive mechanism to grant access to theresources, i.e. is free data transfer capacity. Anti-tokens forbid anode to emit traffic for a given amount of time, thus preserving voidsfor downstream nodes. In more detail, assuming that nodes A, B, C aresupposed to add equal amounts of traffic to the data bus 12, node A mayonly use one third of the data transfer capacity of the data bus 12.Node B may also use one third of the data transfer capacity of the databus 12, and, if present, may also use data transfer capacity of node Athat has not been used. Likewise, node C can access at least one thirdof the data transfer capacity of the data bus 12, and may use, ifavailable, unused data transfer capacity of nodes A, B.

As a result, between nodes A and B the data bus 12 is used to a maximumdegree of one third of its data transfer capacity, and between nodes Band C a maximum of two thirds is used.

The invention provides a fairness mechanism especially dedicated tomultipoint to multipoint networks. Such a network to be used with theinvention is shown FIG. 2. FIG. 2 shows a network 21 comprising fournodes A, B, C, D, and a data bus 22. In the example shown, the data bus22 comprises optical data transfer lines, and at each node all data issubjected to a complete opto-electric conversion.

The overall data flow on the data bus 22 is again from left to right,i.e. is from node A towards node D. The first node A as well as theintermediate nodes B, C may feed data into the data bus 22, as markedwith add A, add B, add C. The intermediate nodes B, C and the node D atthe downstream end of the data bus may drop traffic from the data bus22. After a dropping of data, dropped data is no more transported on thedata bus 22.

In the data network 21, the fairness mechanism, which is based onanti-tokens, is provided to guarantee that the intermediate nodes B, Cmay add traffic to the data bus 22. I.e. the fairness mechanism has toguarantee that nodes B, C also have a minimum data transfer capacity onthe data bus 22 available. As the core of the invention, that fairnessmechanism takes into account drop traffic at the intermediate nodes B, Cwhen allocating data transfer capacity to the adding nodes A, B, C. Dueto the drop function of the intermediate nodes B, C, the remaining (i.e.unused) data transfer capacity (i.e. bandwidth in an optical system)will be increased by the amount of the bandwidth formerly used by droptraffic. In the example above, node C can insert traffic correspondingto the preserved bandwidth rate for that node, it can further useremaining bandwidth originally preserved for previous nodes, and it canuse the bandwidth of traffic dropped at node C. Therefore, thecalculation of TCARD parameters has to consider the amount of droptraffic to increase the total bandwidth utilization.

The drop C traffic bandwidth rate can either be used as spare bandwidthin node C to add traffic which exceeds the reserved add C rate, or theanti-token rate of node C can be reduced by the amount of drop Ctraffic. The latter preserves larger bandwidth capacity in otherfollowed nodes (not shown).

The inventive fairness mechanism for a multipoint-to-multipoint networkcan be extended to logical paths between the nodes. Each logical path ischaracterized by parameters like bandwidth or service level given byservice level agreements (SLA). More important, the logical paths arefurther characterized by a node of origin and a node of destination forthe data transported on that logical path. The fairness mechanism cannow be extended to consider all logical paths and their destinationsinstead of one unique add traffic path per node without considering thedestination. That means, the fairness mechanism will be applied tovarious logical paths in each node. Then the fairness mechanism providesa traffic engineering tool that can organize the amount of trafficbetween the nodes including separating destinations as well as servicelevels to calculate fairness parameters, i.e. anti-tokens for eachlogical path. This fairness mechanism allows the use of bandwidth whichis unused in previous methods.

For example, using FIG. 2, with the proposed extension data traffic canbe inserted into the reserved bandwidth for node C by note A or node Bif the destination of the traffic is known at the add port, and thedestination is node C or an upstream node of node C. So, node A caninsert traffic to node B and/or node C, and node B can insert traffic tonode C. Because this traffic will be dropped in the node C, there willbe no collision with the preserved bandwidth for node C.

As an additional effort, it is necessary to separate the traffic perdestination at each add port. Furthermore, the TCARD mechanism has tohandle more effective add ports. So the TCARD mechanism is used applyingits rules to multiple logical paths with destination separation . As aresult, a very effective bandwidth utilization can be achieved.

FIG. 3 shows a multipoint-to-multipoint network with a TCARDdistribution in accordance with the invention. The data network 31comprises a first node A, a second node B, a third node C, and a fourthnode D. It further comprises a data bus 32 with a data flow directionfrom left to right, that is from node A towards node D. At node A,traffic a is inserted into the data bus 32. Moreover, by means of aTCARD 1, bandwidth is reserved in the data bus 32. At node B, traffic bis added and traffic a′ is dropped from the data bus 32. At node B, aTCARD 2 is applied in order to reserve bandwidth for the following nodeC. At node C, traffic c is added whereas traffic a″ from node A andtraffic b′ from node B are dropped from the data bus 32. At node C,again a TCARD 3 is applied. However, since at node D no traffic isadded, but only traffic is dropped, the TCARD 3 preserves a zerobandwidth. At node D, traffic a′″ originating from node A is dropped,further traffic b″ originating from node B is dropped, and traffic c′originating from node C is dropped. Node D also has formally a TCARD 4,but since no further nodes follow on the bus 32, the TCARD 4 reservesthe bandwidth of zero.

At nodes A, B the TCARDS reserve bandwidth of the data bus 32 forfollowing nodes, that is downstream nodes. Let us now consider TCARD 2:

TCARD 2 is to reserve bandwidth for the add traffic c at node C.Therefore, one of the summands of TCARD 2 is c. Further, at the secondnode B bandwidth is to be reserved for the following nodes, that isnodes C and D. Therefore another summand is TCARD 3 (however, in thiscase, TCARD 3 is zero). At node C traffic a″ and b′ is dropped from thedata bus 32. This causes available data transfer capacity, that isbandwidth, at the data bus 32. So a″ and b′ reduce the bandwidth thatneeds to be reserved at TCARD 2. Therefore, a″ and b′ are subtractedfrom TCARD 2. If said subtractions cause TCARD 2 to become less thanzero, then TCARD 2 is set to zero.

Likewise, the TCARD 1 at node A can be understood. TCARD 1 has toreserve bandwidth for add traffic b at node B, as well as furthertraffic to be added at downstream nodes of node B, that is a bandwidthcorresponding to TCARD 2. However, at node B, traffic a′ originatingfrom node A, will be dropped, reducing the amount of reserved bandwidthneeded downstream of node B. Therefore, the drop traffic a′ can besubtracted from TCARD 1. Again, if the subtraction causes TCARD 1 tobecome less than zero, then TCARD 1 is set to zero.

Following FIGS. 4 to 6 illustrate how a node sends traffic downstream onthe bus, in accordance with the invention. Let us consider node B ofFIG. 3 once more. Node B receives traffic via the data bus 32 from nodeA to be sent downstream; this traffic is called transit traffic.Further, node B adds traffic b to data bus 32. Finally, node B also hasto insert free data transfer capacity on to the data bus 32 asrepresented by TCARD 2.

FIG. 4 shows a quality of service model how to allocate these threesources of traffic at a node to the downstream data bus. The nodecomprises a round robin scheduler 41 which can allocate traffic to thedownstream section of a data bus. In a simple case, where neithertransit traffic nor add traffic are distinguished by priority levels,all in all three traffic sources have to be considered. In the exampleof FIG. 4, a priority order of first transit traffic, second TCARD, andthird add traffic is proposed, in accordance with the invention.

In FIG. 5 a quality of service model distinguishing between premium andbest effort traffic, both in the transit traffic and in the add trafficat a node is considered. The round robin scheduler 51 gives the highestpriority to transit premium traffic, the second priority to TCARD, thethird priority to add premium traffic, the fourth priority to transitbest effort traffic, and the lowest fifth priority to add best efforttraffic. By these means, the average delay time of premium traffic, bothin transit and from other nodes, is minimized. However, best efforttraffic may have to wait at every node on a bus when premium traffic isplentiful.

In FIG. 6 only the add traffic is distinguished by priority levelspremium and best effort. The round robin scheduler 61 gives the highestpriority to transit traffic, the second priority to TCARD, the thirdpriority to add premium traffic, and the lowest and fourth priority toadd best effort traffic. This quality of service model still gives lowaverage delay times for premium traffic, but at the same time avoids theaccumulation of delay times for best effort traffic. This model givesbest effort and premium traffic in transit an equal priority, so besteffort traffic added at a node only has to wait at the node where it isadded. It will not need to wait at further downstream nodes.

Of course, in accordance with the invention, more priority levels thanpremium and best effort can be applied and more complex priority leveldistributions can be handled by a service level agreement protocol. Itis further worth mentioning that a network in accordance with theinvention does not need to comprise only one bus, but may include morecomplex bus systems, in particular with buses of opposite directions ofdata flow. However, to each bus the inventive method with the fairnessmechanism is applied separately.

1. A method for operating a packet based data network, the data networkcomprising a multitude of nodes and a shared data bus, wherein at leastsome of the nodes add traffic to the data bus, and wherein with respectto a data flow in one direction of the data bus, the upstream nodesreserve data transfer capacity of the data bus for downstream nodes bymeans of a fairness mechanism that applies anti-tokens at the nodeswhich add traffic to the data bus, wherein at least some of the nodesdrop traffic from the data bus, said fairness mechanism takes intoaccount the traffic to be dropped at downstream nodes, wherein trafficto be added at a node is split into logical paths where each logicalpath corresponds to a destination node of the added traffic, thefairness mechanism being applied to each logical path to determine thedata transfer capacity available at a node for the respective logicalpaths, where the data bus is a single communication channel connected toeach node that carries all traffic on all of the logical paths, whereinthe anti-tokens forbid a node to emit data traffic for a given amount oftime, thus preserving traffic voids for nodes located downstream todefine reserved data capacity based on data transfer capacity availablefor the logical paths.
 2. A method according to claim 1, whereinreserved data capacity at a node i is R_(i) whereR_(i)=A_(i+1)−D_(i+1)+R_(i+1) for at least some of the nodes, with ibeing a node index number, wherein the index numbers increase indownstream direction of the data traffic; A_(i+1) being added traffic atnode i+1, wherein node i+1 is the neighbouring node of node i on thedata bus in downstream direction; D_(i+1) being dropped traffic at nodei+1; and R_(i+1) being reserved data capacity at node i+1.
 3. A methodaccording to claim 1, wherein a terminal node at the downstream end ofthe data bus, wherein data traffic is only dropped at the terminal node,and no data traffic is added at the terminal node.
 4. A method accordingto claim 1, wherein the fairness mechanism generates anti-tokens foreach of the logical paths.
 5. A method according to claim 1, wherein inat least some of the nodes, transit traffic received from the data busby a node is passed through the node and add traffic received by thenode from another source is added to the data bus, wherein the addtraffic comprises at least two priority levels, and that the fairnessmechanism takes into account the traffic is transit or add traffic, aswell as the priority level of the traffic.
 6. A method according toclaim 5, wherein the node has a priority order of I) transit premiumtraffic II) reserved data capacity for downstream nodes III) add premiumtraffic IV) transit best effort traffic V) add best effort traffic, or apriority order of I) transit traffic II) reserved data capacity fordownstream nodes III) add premium traffic IV) add best effort traffic,wherein I) indicates highest priority.
 7. A method according to claim 1,wherein the add traffic at a node is split into logical paths accordingto the destination of the add traffic, and that a fairness mechanism isapplied to each logical path to determine the data transfer capacityavailable for the respective logical path.
 8. A method according toclaim 7, wherein add traffic of a logical path of a first node with adestination not farther than a second node located anywhere downstreamof the first node is added to the data bus independently from both theadd traffic at the second node and the data capacity to be reserveddownstream of the second node.
 9. A node for adding traffic to a shareddata bus of a packet based data network the node comprising: means fortaking into account the traffic to be dropped at downstream nodes withrespect to a data flow in one direction of the data bus where the databus is a single communication channel that carries all traffic on thedata bus, means for splitting add traffic into logical paths where eachlogical path corresponds to a destination node of the add traffic to becarried by the data bus, and means for applying a fairness mechanism toeach logical path to determine a data transfer capacity available forthe respective path, wherein the fairness mechanism applies anti-tokensat the node, and wherein the anti-tokens forbid the node to emit datatraffic for a given amount of time.
 10. A data network management systemfor operating a packet based data network having a multitude of nodesand a shared data bus, wherein at least some of the nodes add traffic toand drop traffic from the data bus, wherein with respect to a data flowin one direction of the data bus, the upstream nodes reserve datatransfer capacity of the data bus for downstream nodes, the data networkmanagement system comprising: a fairness mechanism that appliesanti-tokens at the nodes which add traffic to the data bus where thedata bus is a single communication channel that carries all trafficamong the nodes, said fairness mechanism taking into account the trafficto be dropped at downstream nodes, means for splitting the traffic to beadded at a node into logical paths where each logical path correspondsto a destination node of the added traffic, the fairness mechanism beingapplied to each logical path to determine the data transfer capacityavailable for the respective logical path, wherein the anti-tokensforbid a node to emit data traffic for a given amount of time, thuspreserving traffic voids for nodes located downstream based on datatransfer capacity available for the logical paths.